1. Field of the Invention
The present invention relates to composite organic filaments, and more particularly, to synthetic (organic resin) filaments reinforced with inorganic extrafine fiber-like segments.
According to the present invention, known extrafine fiber-like segments (e.g., whiskers) are distributed in an organic resin matrix and these materials formed into composite continuous filaments (threads) having a very small diameter, hitherto unobtainable. Each of the composite filaments has a superior strength, stiffness, electrical conductivity, thermal conductivity, sliding, and wear resistance properties. The composite filaments can be used in many fields, for example, spun and woven to form a textile or sheet, formed into a pre-impregnated reinforcement sheet, or cut into short filaments and mixed with resin, cement, and the like.
2. Description of the Related Art
Conventionally obtained fibers or composite fibers are hereinafter discussed in the light of the strength and electrical conductivity, for example, of the fibers. Carbon fibers made from PAN fibers or pitch are well-known as electric conductive fibers, and have a high electrical conductivity, i.e., a specific resistance (.rho.) of 1500 to 2000 .mu..OMEGA.cm. Since the conductivity increases in accordance with the level of graphitization of the carbon fiber, a specific resistance (.rho.) of 800 to 1000 .mu..OMEGA.cm can be attained. Furthermore, since the carbon fibers have a high strength and a high elastic modulus, they are widely used as a reinforcing material for, e.g., sports equipment such as golf clubs, fishing rods, and tennis rackets. Nevertheless, the production processes of the carbon fibers and carbon-fiber-reinforced products are complicated, and thus these fibers are very expensive.
Recently a method of cheaply and efficiently producing carbon fibers by a vapor phase growth process was developed. The carbon fibers produced by vapor phase growth (hereinafter called VGCF's) have superior mechanical properties, such as strength and elastic modulus, and a good electrical conductivity. The level of graphitization of the VGCF's can be increased to obtain a specific resistance (.rho.) of 100 .mu..OMEGA.cm or less and to improve the mechanical properties, but when the VGCF's are produced in a relatively short period, they have a diameter of less than 1 .mu.m and a short length. If the diameter and length of the VGCF's are to be made thicker and longer, a long growth period is necessary which raises the production cost. Therefore, the vapor phase growth process can not economically produce thick and long carbon fibers suitable for practical use.
It is well-known that an electrically conductive powder (filler) such as metal powder and carbon black is mixed with an organic material (synthetic resin) to make the organic material conductive and then the organic material is spun into composite filaments, but the mechanical properties of the obtained filaments are inferior to those of the organic material without the filler. To obtain a practical electrical conductivity of the filaments, it is necessary to mix a large amount of the filler because the filler has a small aspect ratio, and as a result, the mechanical properties of the obtained filaments are reduced. If the carbon fibers made from PAN fibers or pitch are mixed into the organic material (resin) and then the organic material is spun into composite (carbon-fiber-reinforced) filaments, i.e., CFRP's, since each of the carbon fibers has a diameter of 10 .mu.m or more, each of the composite filaments has a diameter of several tens of micrometers or more, and thus has a disadvantage of rigidity.